The anterior olfactory nucleus mediates curious exploration evoked by novel odors

The spontaneous exploratory reaction to novel stimuli reflects a fundamental form of curiosity, which is widely observed in the animal kingdom. How sensory systems mediate the recognition of novel stimuli to evoke exploration is not well understood. To address this question, we presented novel and familiar olfactory stimuli to head-restrained mice, while measuring novelty-evoked exploratory behaviors. In parallel, we recorded neural activity in primary olfactory cortical structures, the anterior olfactory nucleus (AON) or the anterior piriform cortex (aPCx). Novelty strongly modulated odor responses in the AON, but only weakly in the aPCx. Pharmacological and chemogenetic inactivation of the AON but not the aPCx disrupted exploratory responses. During long-term habituation over multiple days, sensory representations were drifting in the AON whereas they became stable within one day in the aPCx. Our findings suggest that AON and aPCx play distinct roles in novelty-evoked exploration. While the AON mediates the immediate reaction to novel stimuli, the aPCx exhibits stable stimulus representations, consistent with supporting odor memory.